Interconnected rubbers stabilized with borates

ABSTRACT

UNVULCANIZED RUBBERY INTERCONNECTED POLYMERS DERIVED FROM LINEAR HOMOPOLYMERS OF CONJUGATED DIENS OF 4 AND 5 CARBON ATOMS AND LINEAR COPOLYMERS THEREOF WITH OLEFINS, ARE STABILIZED WITH TRIALKYL AND TRIARYL BORATES.

Patented Aug. l?, 197i 3,600,351 lIN'lFJERCONNECTED RUBBERS STABILIZED WITH BORATES Jerry Donald Hunt, Cuyahoga Falls, and Robert Paul Spitz, Akron, Ohio, assignors to The Firestone Tire & Rubber Company, Akron, Ohio 7 No Drawing. Filed June 18, 1969, Ser. No. 834,541 Int. Cl. C0811 /02, 11/04 US. Cl. 260--33.6AQ 6 Claims ABSTRACT OF THE DISCLOSURE Unvulcanized rubbery interconnected polymers derived from linear homopolymers of conjugated dienes of 4 and 5 carbon atoms and linear copolymers thereof with olefins, are stabilized with trialkyl and triaryl borates.

This invention relates to stabilizers for rubbery stereoregular homopolymers of conjugated diolefins of 4 and 5 carbon atoms and copolymers thereof with olefins, and more particularly the rubbery copolymer of butadiene and styrene, and especially the unvulcanized, oil-diluted interconnected (or jumped) polymers.

The term polymer is used herein to include homopolymers and copolymers.

The stabilizers of this invention are trialkyl borates (in which the alkyl groups comprise 1 to 10 or 12 carbon atoms in straightor branched-chain hydrocarbon groups or cycloalkyl groups of 4 to 12 carbon atoms) and triaryl borates (in which the aryl groups are phenyl, tolyl, naphthyl, etc.).

From 0.005 to 5 phr. (parts per hundred parts of polymer), and generally 0.1 to 2 phr. of the stabilizer will be used. Less may be used when the stabilizer of the invention is mixed with other stabilizer.

Unvulcanized interconnected rubbery polymers are those in which the viscosity and molecular weight have been jumped or otherwise substantially increased by reaction of the initially produced linear polymer with a suitable reagent to increase the molecular weight and at the same time the branching of the polymer. One type of such reaction is exemplified by the reaction of silicon tetrachloride with a live polybutadiene produced by polymerization of butadiene in a non-aqueous system by means of a lithium-based catalyst (e.g., butyllithium or tetramethylene dilithium), the interconnected polymer containing a silicon atom in the center with four hydrocarbon polymer fragments extending therefrom to form a star. Another type of such interconnecting reaction, termed jumping, is exemplified by the procedure described by E. F. Engel et a1., Rubber Age, December 1964, pages 410-415; any unsaturated rubbery polymer can be jumped by treatment with a two-part catalyst consisting of a Friedel-Crafts catalyst plus a cocatalyst, such as titanium tetrachloride and thionylchloride or ethyl-aluminum sesquichloride and water.

Another type of molecular-weight-increasing-reaction, or interconnecting (jumping) reaction, is exemplified by the reaction of an olefinically unsaturated rubbery polymer with a halogenated organic compound (e.g. ethylene dichloride) in the presence of a strong base (e.g. butyllithium) to produce a mixture of higher molecular weight rubbery polymers of branched construction, and, typically, exemplified by a mixture of polymers having a molecular weight distribution including the original molecular weight of the unreacted rubbery polymer to molecular weights of dimers, trimers, tetramers and higher polymers of the original rubbery polymer. All of these polymers of increased molecular weight contemplated by the invention have improved ability to accept diluting oil and possess good milling and extruding properties (processing properties) when extended with oil. From 10 to 100 parts of processing oil, or thereabout may be added to 100 parts of the polymer.

Difliculty has been experienced in stabilizing many oildiluted rubbery polymers. The stabilizer of this invention provides excellent stabilization of unvulcanized oil-diluted interconnected rubbery polymers, i.e. an unvulcanized linear rubbery polymer which has been interconnected and oil diluted. The invention finds widest use in the stabilization of such copolymers of butadiene and styrene but is useful with other interconnected rubbery polymers, and particularly those derived from the polybutadienes, polyisoprenes and butadiene-isoprene copolymers of any stereo composition. Polymers suitable for use in the interconnecting reaction can be conveniently made by the methods of U8. Pat. No. 3,317,918, for example.

Any of the oils commonly used in the dilution of rubbers can be employed, including particularly higher boiling petroleum fractions such as the commercially known naphthenic and aromatic mineral oils. In the dilution of rubbers with oils, about 37.5 parts of oil are customarily used with 100 parts of polymer, although the amount of oil can vary from 10 to 100 parts, more or less. The oil preferably is added to the polymer after the polymerization and interconnecting reactions are completed. The stabilizer can be added prior to the addition of the oil, it can be added with the oil, or it can be added soon thereafter.

The stabilizer is incorporated into the polymer in the usual manner. The stabilizing effect is recognized by the lessening of the decrease in the viscosity of the polymer on heat aging. The stabilizers are added to protect the polymer during storage and processing. The vulcanizates are useful wherever rubber vulcanizates have been employed, as in the manufacture of tires, hose, and a wide variety of products.

The polymer used in the tests recorded in the following table was prepared by reaction of SiCl, with live butadiene-styrene copolymer obtained through continuous non aqueous polymerization utilizing butyllithium as a catalyst. A polymer cement-oil masterbatch was prepared containing 37.5 parts of processing oil per 100 parts of polymer, and the stabilizers of this invention were added to portions of the masterbatch to produce the samples for aging studies.

These masterbatch samples were desolventized on a drum drier. Each dried polymer masterbatch sample was milled to achieve homogeneity and samples of the appropriate size were cut from each of the milled polymers. A Mooney viscosity (ML/4/ 212 F.) determination was made on each sample prior to aging. Samples containing the various stabilizers were then aged in a forced air oven at C. for various periods of time. The results obtained with the different stabilizers of this invention are recorded in the following table.

PREPARATION OF BORATE The borates may be made by any process. For instance, 3 molecular equivalents of the alcohol or phenol and 1 molecular equivalent of boric acid are placed in toluene (or other suitable solvent) in a flask fitted with a water trap. This is refluxed until no more: Water comes over into the trap. The excess toluene is then removed under vacuum to yield the product, a trialkyl or triaryl borate. Mixed esters may 'be used in carrying out the invention.

Suitable borates include, for example:

Trimethyl borate Triisopropyl borate Trihexyl borates Tri-n-octyl borate Tri-2-0ctyl borate Tridodecyl borates Tricyclobutyl borate Tricyclohexyl borate Triphenyl borate Tritolyl borates Trinaphthyl borates Triphenylmethyl borate Tri(p-octy1phenyl) borate Tris (p-nonylphenyl) borate Polymer samples were prepared with no stabilizer and a commercial stabilizer, and with 0.5 part per hundred parts of polymer of each of the several stabilizers. The results are recorded as comparative Mooney viscosities The tested borates gave better results than the control which contained no stabilizer on aging 3 days.

The stabilized oil-diluted polymers of the invention are useful in practically every instance in which conventional oil-diluted SBR, oil-diluted natural rubber and oil-diluted rubbery polymers have been useful, including, without limitation, use in pneumatic tire treads, sidewalls and carcass stocks. Also the stabilized polymers of the invention can be blended with other known polymers to provide useful commercial compositions for fabrication into useful shapes and articles. The stabilized polymers of the invention are advantageously blended with known rubbers (e.g., natural rubber, polybutadienes, polyisoprenes, butadienestyrene copolymer, isoprene-isobutylene copolymer, polychlorprene, isoprene-styrene copolymer) with or without additional oils, for forming vulcanizates of great technical importance. The novel stabilized polymers are advantageously mixed with the known reinforcing carbon blacks to produce useful commercial stocks, which also can contain one or more additional rubbery polymers, and also can contain 5 to phr. of additional oil or plasticizer. Sulfur and other known vulcanizing agents for natural rubber and the commercial synthetic rubbers are useful for forming vulcanizable stocks containing the novel stabilized polymer. Known methods of mixing, forming, fabricating and curing or vulcanizing compositions of natural and commercial synthetic rubbers are applicable to and useful with compositions containing the novel stabilized polymers of the invention. The novel polymers carcass compositions, and the considerations of this paragraph are especially relevant to the use of the novel polymers in tires.

We claim:

1. Unvulcanized rubbery interconnected polymer derived from linear homopolymers of conjugated dienes of 4 and 5 carbon atoms and linear copolymers thereof with styrene and interconnected by silicon, stabilized with B(OR) in which R is an alkyl group of l to 12 carbon atoms or a cycloalkyl group of 4 to 12 carbon atoms or phenyl, tolyl or naphthyl or an aralkyl or alkaryl group which is a combination thereof.

2. The composition of claim 1 in which the polymer is derived from butadiene-styrene copolymer.

3. The composition of claim 2 in which the polymer is oil diluted.

4. The composition of claim 3 stabilized with tris (phenyl) borate.

5. The composition of claim 3 stabilized with tris (cyclohexyl) borate.

6. The composition of claim 3 stabilized with tris (Z-phenyl-cyclohexyl) borate.

References Cited 7 UNITED STATES PATENTS 2,967,877 1/1961 Groszos 260-448.2 3,131,164 4/1964 Doyle et al. 26045.8 3,244,662 4/ 1966 Strauss et al. 260--29.7 3,422,051 1/ 1969 Carpenter 26033.6 3,450,797 6/1969 Schafer et al 260888 DONALD E. CZAIA, Primary Examiner R. A. WHITE, Assistant Examiner US Cl. X.R. 2604S.7R

'Zggi I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 9 135 Dated August 17, 1971 Inventor) Jerry Donald Hunt and Robert Paul Spitz It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' Col. lines 9 through 12 should read as follows:

--bilized polymers of the invention. The novel polymers are especially useful in pneumatic tire tread, sidewall and carcass compositions, and the considerations of this paragraph are especially relevant to the use of the novel polymers in tires.--

Signed and sealed this 28th day of March 19 72.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

